George richards



G. RICHARDS.

CUTTER OR HOB FOR MILLING SCREW THREADS.

, APPLICATIONIHLED AUG.14,1918- 1,306,855; Pa-tenfed June 17, 1919.

GEORGE RICHARDS, OF WESTMINSTER, LONDON, ENGLAND.

CUTTER OR HOB FOR MILLING SCREW-THREADS.

Application filed August 14, 1918.

To all whom it may concern:

Be it known that I, GEORGE RICHARDS, a citizen of the United States, residing at the Outer Temple, 222 Strand, in the city of Westminster, London, England, have invented new and useful Improvements in Cutters or Hobs for Milling Screw-Threads, of which the following is a specification.

This invention relates to rotary cutters of the hob type for milling screw-threads; that is to say, cutters which, in order to cut the threads to the required depth, are capable of being advanced in' a direction at right angles to the axis of the work, but partake of no longitudinal movement in a direction parallel thereto.

In the specifications to British Letters Patent granted to me, and dated 15th October, 1915, No. 14571 25th November, 1915, No. 1667 9, and 15th January, 1916, No. 103318, are described means whereby, in milling screw-threads with the aid of hobs, the formation of facets upon the work is prevented. My present invention relates to simplified means whereby the formation of such facets is prevented; same consisting in moving the hob laterally in a plane approximately parallel with a tangent of the workplece.

In the accompanying drawing, A represents the work-piece and B the hob. The former rotates on a fixed axis in the direction of the arrow (4. The latter revolves in the same direction and at the same rotative speed, but on an axis which is capable of lateral motion in the direction of the arrow 1). So long as the axes of the two bodies maintain the same relative positions, their rotative speeds being equal, each tooth of Specification of Letters Patent.

Patented June 17, 1919.

Serial No. 249,891.

the cutter will, in the course of its rotation, arrive at the same point of contact in the periphery of the work-piece, with the result that facets are formed in the surface of the latter as shown. If, however, the axis of the cutter be gradually moved in the direction of the arrow Z) a distance corresponding with the pitch of the teeth-points, the cutting action of each tooth comes into operation somewhat earlier at each revolution, with the result that the facet-making effect is eliminated or avoided. The same lateral movement of the cutter is continued until its axis arrives in the vertical plane of the work-piece, with the object of cutting the thread in the latter to its full depth.

In my aforesaid previous specifications, the creep in advance motion for the avoidance of facets was effected by an angular movement of the hob about its own axis.

According to the herein described method of accomplishing the same object, the hob, in moving laterally, partakes of a rectilinear motion; but it may, if preferred, be caused to move through an arc of a circle whereof the center is either above or below that of the work.

I claim In milling screw threads with the aid of a rotary cutter of the hob type, the herein described means whereby the teeth of the cutter are advanced to the full depth of the thread to be out, and the formation of facets upon the surface of the work is at the same time prevented; same consisting in imparting to the work a relative lateral movement in a direction approximately at right angles to a line connecting their respective centers.

GEORGE RICHARDS.

Copies of this patent may be obtained for five cents each, by addressing the Commissioner of Patents, Washington, D. C. 

